Two ways to grow new tomato plants from ones you already have
You can start new tomato plants in two ways: from cuttings (pieces of stem from a living plant) or from seeds saved from ripe fruit. Cuttings are faster—they produce a flowering plant in 6 to 8 weeks—but seeds give you more plants from less material. Both methods work indoors on a sunny windowsill or under grow lights, and neither requires special equipment beyond a jar, soil, and a sharp knife.
The choice depends on what you have available. If you already grow tomatoes and want to clone a plant you like, cuttings are the practical choice. If you want to save seeds from this year's harvest to plant next spring, that takes longer but costs almost nothing and stores easily.
Key Takeaways
- Tomato cuttings root in water in 7 to 14 days and can move to soil once roots are half an inch long.
- Take cuttings from the top 4 to 6 inches of a healthy stem, remove the lower leaves, and place the cut end in water or moist soil.
- Seeds must dry completely before storage and should be started indoors 6 to 8 weeks before your last spring frost.
- Cuttings root best in warm conditions (65 to 75 degrees Fahrenheit) with bright indirect light, not direct sun.
- A cutting from a determinate tomato variety will grow into a determinate plant; the same is true for indeterminate varieties.
Rooting tomato cuttings in water
Cut a 4- to 6-inch section from the top of a healthy stem, using a clean knife or pruners. The cutting should have at least two sets of leaves. Remove all leaves from the bottom 2 inches of the stem—these would rot if they sat in water. Leave the top leaves intact; they feed the cutting while roots form.
Place the cut end into a jar of room-temperature water, making sure no leaves touch the water surface. Set the jar on a windowsill with bright indirect light (not direct sun, which can overheat the water and cause rot). Change the water every 2 to 3 days to keep it oxygenated. Roots usually appear in 7 to 14 days. Once roots reach half an inch long, the cutting is ready to move to soil.
If the cutting wilts in the first few days, mist the leaves with water and move it slightly away from the light source. Wilting usually means the cutting is losing water faster than the developing roots can replace it. This is normal and temporary.
Moving rooted cuttings to soil
Fill a small pot (3 to 4 inches wide) with moist potting soil. Make a hole with your finger about an inch deep. Gently place the rooted cutting into the hole and firm the soil around it. Water lightly so the soil is damp but not soggy.
Set the pot in bright indirect light and keep the soil consistently moist for the first week. After 7 to 10 days, the cutting will have adjusted to soil and you can water it less frequently—only when the top inch of soil feels dry. Once the plant is 6 inches tall and has several sets of true leaves, it can move to a larger pot or outdoors if temperatures stay above 50 degrees Fahrenheit at night.
Saving and starting seeds from tomatoes
Let a ripe tomato sit at room temperature for 2 to 3 days after you pick it. Cut it in half and scoop the seeds and gel into a small container. Add a little water and let the mixture sit for 2 to 3 days at room temperature—this fermentation breaks down the gel coating that prevents germination. Stir it once a day.
Pour the mixture through a fine strainer and rinse the seeds under running water until they are clean and the gel is gone. Spread the seeds on a paper towel or coffee filter and let them dry completely in a warm, dry place out of direct sun. This takes 1 to 2 weeks. Once dry, store the seeds in an envelope in a cool, dark place (a refrigerator works well) until spring.
To start seeds indoors, fill a seed tray or small pots with moist seed-starting mix. Press seeds into the soil about a quarter inch deep—tomato seeds need light to germinate, so do not cover them completely. Mist the soil with water and cover the tray with a humidity dome or plastic wrap. Keep the soil warm (70 to 80 degrees Fahrenheit) and moist. Seeds sprout in 5 to 10 days. Once they emerge, remove the cover and place them under grow lights or on a very sunny windowsill.
Light and temperature for young plants
Seedlings and rooted cuttings grow best under bright light for 14 to 16 hours a day. A sunny south-facing window works if the light is strong enough that you can read by it at midday. If the seedlings look pale or stretch toward the light, they need more brightness—move them closer to the window or add a grow light 4 to 6 inches above the plants.
Keep temperatures between 65 and 75 degrees Fahrenheit during the day. At night, temperatures can drop to 55 to 60 degrees, which actually strengthens the plants. Avoid placing pots near heating vents, cold drafts, or direct sun through glass, which can overheat them. Once seedlings have their first true leaves (the second set to emerge), you can begin feeding them with a diluted liquid fertilizer every 7 to 10 days.
Hardening off before moving plants outdoors
Young tomato plants grown indoors are tender and will wilt or die if moved directly into outdoor sun and wind. Harden them off by gradually exposing them to outdoor conditions over 7 to 10 days. Start by placing them in a shaded, sheltered spot outdoors for 2 to 3 hours. Each day, increase the time outside and move them into brighter light. By day 7 or 8, they should tolerate full sun and outdoor temperatures.
Begin hardening off about 1 to 2 weeks before your last spring frost date. Transplant seedlings into the garden only after the soil has warmed to at least 60 degrees Fahrenheit and nighttime temperatures stay above 50 degrees. Cold soil and air slow growth and can stunt the plants permanently.
Common mistakes and how to avoid them
The most common error is overwatering. Soil that stays soggy causes root rot in both cuttings and seedlings. Water only when the top inch of soil is dry. The second mistake is too little light, which makes plants pale and spindly. If you cannot provide 14 hours of bright light daily, a straightforward LED grow light is inexpensive and makes a real difference.
Do not fertilize seedlings until they have their first true leaves, and do not use full-strength fertilizer—dilute it to half strength. Fertilizing too early or too strong burns the roots. Finally, do not rush hardening off. Plants moved outdoors too quickly often stop growing or die, even if they look healthy indoors.
Frequently Asked Questions
Can I propagate tomatoes from a store-bought tomato?
Yes, if the tomato is not a hybrid. Most grocery store tomatoes are hybrids, and seeds from them will not grow into plants identical to the parent. Heirloom and open-pollinated varieties produce seeds that grow true. If you are unsure, try it anyway—the worst outcome is a plant that looks different from what you expected.
How long does it take a cutting to become a full-size plant?
A rooted cutting becomes a flowering plant in 6 to 8 weeks indoors, and produces fruit 2 to 3 weeks after flowers appear. From cutting to first ripe tomato is usually 10 to 12 weeks. Seedlings take longer—12 to 16 weeks from seed to first fruit—but you get more plants from the same effort.
Can I root a cutting in soil instead of water?
Yes. Use moist potting soil or a mix of peat moss and perlite. Keep the soil consistently damp (not soggy) and cover the pot with a humidity dome or plastic bag for the first week. Rooting takes slightly longer in soil than in water, usually 10 to 21 days, but you skip the step of moving the cutting to soil later.
What if my cutting gets mold or turns brown in water?
Brown or mushy stems mean the cutting is rotting, usually from water that is too warm or too stale. Change the water when ready, trim off any brown parts with a clean knife, and move the jar to a cooler spot. If most of the cutting is brown, discard it and start over with a fresh cutting.
Do I need to use rooting hormone?
No. Tomato cuttings root easily in plain water or moist soil without any rooting hormone. Hormone can speed rooting slightly, but it is not necessary and adds cost. Save it for plants that are harder to propagate.